For hiking (usually ~6-8 hours), I take a hydration pack with 2 liters of water mixed with 4 Nunn tablets (non-caffeinated). I usually take some iodine tablets and refill from a stream. When I was younger I never bothered with the iodine and would drink straight from a stream but got more paranoid as I got older.
For splitboarding (similar duration), I normally take a 1 liter collapsible water ‘bottle’ and a flask with 0.5 liters of herbal tea.
My impression is I need at least ~0.5 liters of fluids per hour but don’t always get this and normally come back thirsty. For that reason, I try to take extra water and tea and leave them in the car for when I get back.